Plywood panel faced with metal and method of making the same



Aug. Is, 1925.

' A. ELMENDORF PLYWOOD'PANEL moan WITH METAL AND METHOD OF MAKINGTHE SAME Filed July 11. 1923 .INVENTOR;

A TORNEYS.

Patented Aug. 18, 1925.

Paramorrilca.

ARMIN' ELMENDORF, O'F'CHICAGO, ILLINOIS.

PLYWOOD PANEL FACED WITH METAL AND METHOD OF MAKING THESAME.

Application filed July 11, 1923. Serial No. 650,871.

To all whom it may concern:

Be it known that LARMIN ELMENDORF, a citizen of the United States, residing at Chicago, county of Cook, State of Illinois, have invented a certain new and useful Improvement in Plywood Panels Faced with Metal and Methods of Making the Same, and declare the following to be a full, clear, and exact description of the same, such as will enable others skilled in the art to which it pertains to make and use the same, reference being had to the accompanying drawing, which forms'a part of this specification.

In the use of plywood panels'that is panels made of a plurality of layers of wood glued together for such exposed places as on the sides of commercial bodies, omnibus bodies, and for outdoor signs, considerable trouble is experienced from the checking of the face veneer. This applies even when so-called waterproof glues are used, as Well as when the surface is given a high grade paint finish. YVhen the paint has developed cracks, be they ever so small, they tend to mcrease in size with the eventual penetration of the moisture into the plywood, causing the plys to separate and the panel to disintegrate. This difliculty has been overcome by gluing a thin sheet steel plate on one or both faces of the plywood panel. In the case of commercial automobile bodies and similar uses of plywood panels it is necessary to keep the weight of the panel sides down to a minimum so that the steel can pnly be applied on the outside or exposed ace.

The gluing of a sheet steel plate to one face of the plywood panel introduces a se rious objection. When such a panel is exposed to changes-in atmospheric humidity the moisture content of the plywood changes, causing it to expand or contract very slightly. The face which is constrained by the steel or metal sheet cannot expand or contract, so that the panel warps.

Another objection to the gluing. of steel sheets to plywood lies in the limitation in sizeof the resultantv panel, which cannot be made larger than the maximum size in whichthe thin steel sheets can be rolled, for it is practically impossible to make satisfactory joints between two such sheets. It is very difficult. to lay' the steel sheets edge to edge during the gluing operation,

' sheets, of steel.

' the result being that a closed butt joint cannot be obtained. If the steel sheets are overlapped slightly, a bulge or ridge in the surface results which ridge cannot be concealed by the usual high grade finish procedures, nor can it be effectively compressed into the plywood panel by pressure or rolling. As a consequence it becomes quite impossible to provide large plywood panels with a facing constituted by thin If the glue 'is omitted in the lap of one steel sheet over the adjacent sheet'and the attempt is made to bend the lap back at a sharp angle, the steel is either pulled away from the plywood or the'bend is not sharp enough to make a satisfactory joint after the overlapping portion is cut off.

Tests have been made to determine the effectiveness of covering plywood surfaces with extremelythin aluminum leaf. .When these test panels were exposed to the weather, checking and disintegration followed in the same manner as described for an ordinary painted plywood surface.

The present invention has for its object to produce improved plywood sheets or panels coated with metal, and particularly sheets or panels of largedimensions coated with metal in a plurality of sheets. The invention consists, broadly, in the employment of sheet metal of sufficient th ckness to protect the surface of the wood, ex-

be applied so as to form lap joints or butt joints. If lap joints are formed, the-joints may be pressed, rolled or burnished in order to render them less apparent; as, with metal of a thickness of the order above indicated, the general'surface of thejwood may be depressed withoutmaterially injuring its structure by; such operations. Aluminum and tin are examples of metals that may successfully be used in practicing my invention. The thickness of. the metal in the sheets depends not so much on the character of the metal ason the character of the anel to which the sheets are to be applied. ome

must be used in sheathing panels made of wood that is apt to check considerably.

In forming butt joints, the metal sheets are preferably applied to the wood so that the edge of one sheet will overlap the adjacent edge of the next sheet without, however, the overlapping portions not being cemented together. The free portion of the sheet is then detached by any suitable means.

Such detachment is conveniently effected by bending the free .portion sharply back and severing it along the line of the joint from the remainder of the sheet by means of a knife.

In carrying the invention into effect with a view to securing butt joints between the metal sheets, the surface of the plywood is coated with a suitable glue. The sheets of metal are then applied, the second sheet and following sheets being arranged to overlap the preceding sheets. The portion of a sheet overlapping a preceding sheet will of course not adhere thereto, as only the surface of the wood will be coated with adhesive. After the glue has set, the lap or flap which is unglued can be bent back to a very sharp bend at the exact edge of the underlying sheet of metal. The conventional glues are of suflicient strength when this is done to enable a very sharp bend to be made. Metal sheets up to about 0.05 mm. in thickness are satisfactory in this respect. The spread and consistency of the glue in the process described must be such that when roller pressure is applied, the glue does not fiow under the squeezin action of the roll. It has been found possib e to apply the glue of such a consistency and at the same time to make the spread so thin that the glue will not flow and in this way produce laps and wrinkles in the metal covering, nor will it spread over the edge of the underlying sheet of metal in the lap joint. The glue on the other hand must retain a certain consistency in order to be effective as an adhesive. This result is best obtained by using a modified casein glue of a fairly thick consistency, spreading, then rolling off superfluous glue under pressure and then allowing the surface moisture to evaporate to slight extent, after which the metal is quickly applied by meansof rolls.

. With some metals superior binding of the metal to the wood is obtained if the panels to which the metal has been applied as described are subsequently subjected to pressure between plates.

When lap joints are-made with metal of the thickness specified in the above example and the laps are glued and then pressed, rolled, or burnished, the lap joints can be effectively concealed with the conventional finish procedures. By conventional finish procedures are meant the finishes used ordinarily for the side panels of commercial automobile bodies or the like. On the other hand, when the metal is very much thinner than 0.006 mm. the splitting and checking of the paint is liable to ensue at joints in the underlying veneer or at mill checks. For each metal there therefore exists a thickness range which makes it possible to metalize plywood panels of any size without obtaining splits or checks in the finish, and at the same time making it possible to produce a joint in the metal coating which can be effectively and completely concealed by the conventional finish procedures. This thickness range varies with different metals.

Plywood or wood pulp panels provided wit-ha metal coating in accordance with the invention, on one face only, do not warp like similar panels covered on one face with a thin sheet of steel. This is no doubt due to the fact that the veryslight expansion of the panel under absorption of moisture from the air causes a slight elastic stretch of the thin metal sheet used;

While the invention pertains primarly to plywood panels, other panels equally soft such as those made of wood pulp or sugar cane fibers may be coated by the same methods with the same results.

My invention is illustrated more or less diagrammatically in the accompanying drawing, wherein: Figure 1 is an edge view of a fragment of a panel, showing the first step in producing a lap joint between ad acent metal facing sheets, the thickness of the parts being greatly exaggerated; Fig. 2 is a view similar to Fig. 1, showing the completed product; and Figs. 3 and 4 are views similar to Fig. l and Fig. 2, respectively, illustrating the method of making a butt joint between two metal facing sheets.

Referring to Figs. 1 and 2 of the drawing, 1 is a plywood panel and 2 and 3 are two thin facing sheets of metal of the character heretofore explained, glued to the panel. The sheet 2 has a marginal portion 4: which overlaps and is glued to the sheet 3. When the lap joint is rolled, that part 5 of the sheet 3 underlying the overlapping portlon 4 is pressed inwardly into the wood of the panel so that the part 1 is again brought into the normal plane of the two sheets, as shown in Fig. 2.

In Fig.3 the parts are the same as in Fig. 1 except that the part 4 is not glued to the sheet 3. Therefore, after the metal sheets have been glued to the panel which at that time has the same appearance as in Fig. 1, the marginal portion 4 may be bent outwardly at a sharp angle, retaining contact with the edge of the sheet 3, as shown in Fig. 3, and then be cut ofi, causing the panel to appear as shown in Fig. 4.

It will be seen that in each example of my invention illustrated, the sheets of metal are glued to the" panel so as first to make an overlapping joint, and this joint is then reduced, either by pressing the under layer of metal at the joint into the veneer or by cutting away the outer layer in such a manner that a smooth, substantially continuous surface results.

I claim:.

1. The method of facing a plywood or fiber board panel with metal, which consists in gluing to said surface metal sheets so thin that sections may be pressed into the panel to a depth-equal approximately to the thickness of the metal, or that the metal without structural injury to the panel may be bent to form substantially a sharp corner edge, so as to cause a marginal portion of one sheet to overlap an adjacent sheet, sharply bending said marginal portion back while maintaining edge contact between the said sheets throughout the length thereof, and then cutting away such marginal portion along a line in the plane of the exposed surface of the sheets.

2. 'A plywood or' fiber board panel faced with a multiple number of metal sheets arranged edge to edge glued thereon, the metal having a thickness not greater than 0.05 mm. nor less than 0.006 mm.

3. A plywoodpanel having glued thereto a metal facing composed of sheets thin enough to have sufficient elastic stretch to permit the panel to expand and contract normally and thick enough to withstand the stresses which cause checking in the surface finishes usually applied to wooden panels, said sheets being engaged with each other at their edges.

4. A plywood or fibre board panel faced with a multiple number of metal sheets arranged edge to edge and glued thereon, the metal being thin enough to have sufficient elastic stretch to permit the panel to expand and contract normally, and having a thickness not less than 0.006 mm.

A plywood or fibre board panel faced with a multiple number of metal sheets arranged edge to edge and glued thereon, the metal having a'thickness not greater than 0.05 mm. butsufiiciently great to withstand the stresses which cause checking in the surface finishes usually applied to wooden panels.

In testimony whereof, I sign this specification.

ARMIN ELMENDORF. 

